Injection apparatus

ABSTRACT

In an injection apparatus, a first cylinder and second cylinder for driving an injection cylinder connected to an injection plunger are connected in parallel with each other with respect to the injection cylinder. A piston of the first cylinder and a piston of the second cylinder are synchronously driven by driving means. A directional control valve and flow rate adjustment circuit are provided between one end of the injection cylinder and one end of the first cylinder.

TECHNICAL FIELD

The present invention relates to an injection apparatus.

BACKGROUND ART

Injection apparatuses are known as an apparatus that injects a moldingmaterial into a mold and fills the mold with the molding material toform a desired product. As in the injection apparatus disclosed inPatent Document 1, for example, recent injection apparatuses applyactuating force to an injection cylinder by using an electric motor. Theinjection apparatus of Patent Document 1 includes an injection cylinderdevice for actuating an injection plunger to inject a molding materialinto a mold, and a conversion cylinder device for supplying hydraulicoil to the injection cylinder device. In the injection apparatus ofPatent Document 1, an electric motor is used as the driving source todrive the conversion piston of the conversion cylinder device whensupplying the hydraulic oil to the injection cylinder. In the injectionapparatus of Patent Document 1, therefore, the driving force of theelectric motor actuates the conversion piston of the conversion cylinderdevice to supply the hydraulic oil to the injection cylinder device, andthen the supplied hydraulic oil actuates the injection piston of theinjection cylinder device in the direction in which the molding materialis to be injected.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: Japanese Patent Application Laid Open No. 2010-115683

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

However, an injection apparatus is generally actuated in three steps: alow-speed step, a high-speed step, and a pressure increasing step. Ineach of these steps, the injection piston is actuated at a desired speedto apply a desired pressure to a molding material inside a cavity.Therefore, actuating the operating cylinder by the driving force of theelectric motor, as in the injection apparatus of Patent Document 1,enables more accurate control of the operating quantity of the injectioncylinder than when actuating the operating cylinder by only controllingthe flow rate of the hydraulic oil by means of a hydraulic pump or thelike. However, since the injection apparatus of Patent Document 1 usesdifferent driving means between the speed control steps and the pressurecontrol step of the above steps, driving means are required for theabove control steps respectively. This not only increases the number ofparts of the injection apparatus but also makes the structure of theinjection apparatus complicated and large.

The present invention was conceived in view of the foregoing problems,and an object of the present invention is to provide an injectionapparatus capable of realizing high injection speed and high injectionpressure by means of a single unit of driving means.

Means for Solving the Problem

In order to solve the above problem, the present invention includes: aninjection cylinder that drives an injection plunger to inject a moldingmaterial; a first cylinder that is connected to the injection cylinderand feeds hydraulic oil to the injection cylinder and drains hydraulicoil from the injection cylinder; a second cylinder that is connected tothe injection cylinder in parallel with the first cylinder and feedshydraulic oil to the injection cylinder and drains hydraulic oil fromthe injection cylinder; a single unit of driving means forreciprocatingly driving a piston of the first cylinder and a piston ofthe second cylinder; a directional control valve that is providedbetween one end of the injection cylinder and one end of the firstcylinder and allows a flow of hydraulic oil from the first cylindertoward the injection cylinder but cuts off the flow of hydraulic oilfrom the injection cylinder toward the first cylinder; and flow rateadjustment means that is provided between the directional control valveand the first cylinder and that is for adjusting a flow rate ofhydraulic oil between the one end of the first cylinder and the one endof the injection cylinder, wherein the driving means drives the pistonof the first cylinder and the piston of the second cylinder insynchronization with each other.

Advantageous Effect of the Invention

The present invention can provide an injection apparatus capable ofrealizing high injection speed and high injection pressure by means of asingle unit of driving means.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 This drawing shows a circuit diagram of an injection apparatus ofthe present invention.

MODE FOR CARRYING OUT THE INVENTION

An injection apparatus according to an embodiment of the presentinvention is described hereinafter.

A die-casting machine functioning as an injection apparatus is anapparatus for injecting a metallic material (e.g., aluminum) as a moltenmolding material into a cavity that is formed by a fixed mold andmovable mold configuring a mold, and then filling the cavity with themetallic molding material. The molding material that is injected intothe mold is solidified and then demolded, resulting in a desired moldedarticle. Referring to FIG. 1, a die-casting machine 100 includes aninjection cylinder 1. The injection cylinder 1 is a cylinder forinjection-driving an injection plunger to force, into the cavity, themetallic material that is supplied to an injection sleeve communicatedto the cavity. The injection plunger is connected to a tip end of apiston rod 1Pa of a piston 1P in the injection cylinder 1. Aacceleration cylinder 2 as the first cylinder and a booster cylinder 3as the second cylinder, which feed and drain hydraulic oil as anincompressible fluid (fluid), are connected to the injection cylinder 1via piping. A bottom chamber 2B of the acceleration cylinder 2 isconnected to a bottom chamber 1B of the injection cylinder 1.Furthermore, a bottom chamber 3B of the booster cylinder 3 is connectedto the bottom chamber 1B of the injection cylinder 1 in parallel withthe bottom chamber 2B of the acceleration cylinder 2. In the presentembodiment, the stroke of a piston 2P of the acceleration cylinder 2 andthe stroke of a piston 3P of the booster cylinder 3 are set at the samelength. The diameter D2 of the acceleration cylinder 2 is set to begreater than the diameter D3 of the booster cylinder 3. The piston 2P ofthe acceleration cylinder 2 is connected to a nut 12 via the rod chamber2R. The piston 3P of the booster cylinder 3 is connected to the nut 12via the rod chamber 3R. A ball screw 11 is fitted into the nut 12. Theball screw 11 can freely be rotated by a motor 10. In the presentembodiment, a servomotor is used as the motor 10. The ball screw 11 andthe nut 12 configure a ball screw mechanism. The nut 12 is configured tomove in the right-left direction on FIG. 1 as the ball screw 11 rotates.The piston 2P and the piston 3P can be freely reciprocated in theacceleration cylinder 2 and the booster cylinder 3 respectively by thenut 12. In the present embodiment, the piston 2P and the piston 3P areconnected to the nut 12 in such a manner as to synchronously move by thesame moving quantity when the nut 12 moves. Further, in the presentembodiment, the motor 10, the ball screw 11 and the nut 12 configure adriving means. The driving means in the present embodiment is a singleunit.

A pilot operated check valve 4 as a directional control valve isprovided on the pipe between the bottom chamber 1B located at one end ofthe injection cylinder 1 and the bottom chamber 2B located at one end ofthe acceleration cylinder 2. The pilot operated check valve 4 allowshydraulic oil to flow from the bottom chamber 2B of the accelerationcylinder 2 toward the bottom chamber 1B of the injection cylinder 1. Thepilot operated check valve 4 also cuts off the flow of the hydraulic oilfrom the bottom chamber 1B to the bottom chamber 2B. Note that a pilotconduit 4P is connected to the pilot operated check valve 4 in thepresent embodiment. The pilot conduit 4P is a conduit for introducingpressure in the pipe, which connects the rod chamber 1R of the injectioncylinder 1 to a feed/discharge mechanism 20 (to be describedhereinafter), to the pilot operated check valve 4. Thus, when the pilotpressure is applied from the pilot conduit 4P to the pilot operatedcheck valve 4, the pilot operated check valve 4 can be opened to allowthe flow of the hydraulic oil from the bottom chamber 1B to the bottomchamber 2B. A flow rate adjustment circuit 5 as the flow rate adjustmentmeans is provided between the pilot operated check valve 4 and thebottom chamber 2B of the acceleration cylinder 2. The flow rateadjustment circuit 5 is provided with a buffer tank 15, a pilotswitching valve 16 and a check valve 6. The buffer tank 15 temporarilystores enough hydraulic oil to adjust any excess and deficiency ofhydraulic oil in the acceleration cylinder 2. The check valve 6 isprovided on a pipe that extends from the buffer tank 15 to the pipebetween the pilot operated check valve 4 and the bottom chamber 2B ofthe acceleration cylinder 2. The check valve 6 cuts off the flow ofhydraulic oil from the pipe between the pilot operated check valve 4 andthe bottom chamber 2B of the acceleration cylinder 2 to the buffer tank15. Also, the check valve 6 allows the hydraulic oil to flow from thebuffer tank 15 to the pipe between the pilot operated check valve 4 andthe bottom chamber 2B of the acceleration cylinder 2. The check valve 6is a hydraulic oil replenishment control valve for appropriatelysupplying the hydraulic oil of the buffer tank between the pilotoperated check valve 4 and the bottom chamber 2B of the accelerationcylinder 2 when the hydraulic oil between the pilot operated check valve4 and the bottom chamber 2B of the acceleration cylinder 2 becomesinsufficient. The pilot switching valve 16 is provided on a pipe thatextends from the pipe between the pilot operated check valve 4 and thebottom chamber 2B of the acceleration cylinder 2 to the buffer tank 15.The pilot switching valve 16 is a valve for switching between acommunicated state and a cut off state of the flow of hydraulic oil fromthe pipe between the pilot operated check valve 4 and the bottom chamber2B of the acceleration cylinder 2 to the buffer tank 15. The pilotswitching valve 16 is normally biased to its cut off position by aspring. A pilot conduit 16P is connected to the pilot switching valve16. The pilot conduit 16P is a conduit for introducing, to the pilotswitching valve 16, pressure in the pipe located between the bottomchamber 1B of the injection cylinder 1 and the pilot operated checkvalve 4 and bottom chamber 3B of the booster cylinder 3. The pilotswitching valve 16 is switched when the pilot pressure introduced fromthe pilot conduit 16P becomes greater than the biasing force of thespring. The pilot switching valve 16 discharges the hydraulic oil to thebuffer tank 15 when switched to the communicated state. In the presentembodiment, the pilot pressure is set at a value smaller than themaximum pressure that can be applied by the acceleration cylinder 2 andthe booster cylinder 3.

The feed/discharge mechanism 20 is connected to the rod chamber 1R ofthe injection cylinder 1. The feed/discharge mechanism 20 is a hydrauliccircuit for feeding the hydraulic oil to the rod chamber 1R anddischarging the hydraulic oil from the rod chamber 1R. Thefeed/discharge mechanism 20 is configured by an electromagneticswitching valve 21, a hydraulic pump 22, and a hydraulic oil tank 25.The electromagnetic switching valve 21 switches the condition of thepipe connecting the rod chamber 1R of the injection cylinder 1 and thehydraulic oil tank 25 to each other. The hydraulic pump 22 is providedon the pipe between the electromagnetic switching valve 21 and thehydraulic oil tank 25. The hydraulic pump 22 is a pump for supplying thehydraulic oil in the hydraulic oil tank 25 to the rod chamber 1R of theinjection cylinder 1.

The actions of the present embodiment are described next.

The injection apparatus 100 drives the injection cylinder in order toinject a molding material by means of the injection plunger. In sodoing, the injection apparatus 100 supplies the hydraulic oil to thebottom chamber 1B of the injection cylinder 1 in order to expand thebottom chamber 1B by moving the piston 1P of the injection cylinder 1.The injection apparatus 100 first drives the motor 10 to rotate the ballscrew 11. Consequently, the nut 12 fitted onto the ball screw 11 ismoved toward the left side on FIG. 1, more specifically, is moved toapproach the acceleration cylinder 2 and the booster cylinder 3. Whenthe nut 12 is moved, the pistons 2P and 3P connected to the nut 12 aremoved within the acceleration cylinder 2 and booster cylinder 3,respectively. The pistons 2P and 3P are driven in synchronization witheach other and moved an equal distance. When the piston 2P is moved inacceleration cylinder 2, the hydraulic oil in the bottom chamber 2B ofthe acceleration cylinder 2 is supplied toward the injection cylinder 1.The hydraulic oil discharged from the bottom chamber 2B passes throughthe pilot operated check valve 4 and flows to the bottom chamber 1B ofthe injection cylinder 1. At this moment, the hydraulic oil dischargedfrom the bottom chamber 2B does not flow to the flow rate adjustmentcircuit 5. In the flow rate adjustment circuit 5, the pilot switchingvalve 16 is biased to its cut off position by the spring. In addition,the check valve 6 cuts off the flow of the hydraulic oil from the bottomchamber 2B to the buffer tank 15. When the piston 3P is moved in thebooster cylinder 3, the hydraulic oil in the bottom chamber 3B of thebooster cylinder 3 is supplied toward the injection cylinder 1. Thehydraulic oil discharged from the bottom chamber 3B flows to the bottomchamber 1B of the injection cylinder 1 together with the hydraulic oildischarged from the bottom chamber 2B of the acceleration cylinder 2.Here, the feed/discharge mechanism 20 causes the electromagneticswitching valve 21 to communicate the rod chamber 1R with the hydraulicoil tank 25 so that the hydraulic oil in the rod chamber 1R can bedischarged to the hydraulic oil tank 25. In the injection cylinder 1,the hydraulic oil is supplied from both the acceleration cylinder 2 andthe booster cylinder 3 to the bottom chamber 1B, and the hydraulic oilof the rod chamber 1R is discharged to the hydraulic oil tank 25,thereby moving the piston 1P at high speed. As a result, the injectionplunger is injection-driven at high speed.

The cavity becomes filled with the molding material as the injection ofthe molding material at high speed is implemented by the injectioncylinder 1 and the injection plunger. Once the cavity becomes filledwith the molding material, resistance against the direction in which thepiston 1P moves occurs in the injection plunger and the injectioncylinder 1. Consequently, the pressure of the hydraulic oil in thebottom chamber 1B of the injection cylinder 1 is increased by thehydraulic oil supplied from the acceleration cylinder 2 and the boostercylinder 3. The injection apparatus 100 continues to drive the motor 10to continuously supply the injection cylinder 1 with the hydraulic oilfrom the acceleration cylinder 2 and the booster cylinder 3. Thepressure within the pilot conduit 16P is increased as the pressurewithin the bottom chamber 1B is increased. When the pressure within thepilot conduit 16P exceeds a predetermined value, the pilot switchingvalve 16 switches from the cut off position to the communicatingposition. Then, the hydraulic oil discharged from the bottom chamber 2Bof the acceleration cylinder 2 is caused to flow and discharged to thebuffer tank 15 via the pilot switching valve 16, because the pressure ofthe hydraulic oil between the bottom chamber 1B of the injectioncylinder 1 and the pilot operated check valve 4 becomes higher than thebuffer tank 15. On the other hand, the hydraulic oil supplied from thebottom chamber 3B of the booster cylinder 3 pressurizes the hydraulicoil within the bottom chamber 1B of the injection cylinder 1. Themolding material within the cavity therefore continues to bepressurized. Moreover, the hydraulic oil supplied from the bottomchamber 3B is prevented by the pilot operated check valve 4 from flowingto the buffer tank 15. In the injection cylinder 1, when the pressurewithin the bottom chamber 1B becomes equal to or greater than the pilotpressure of the pilot switching valve 16, only the hydraulic oil of thebooster cylinder 3 is supplied to the bottom chamber 1B. This makes thesupply of hydraulic oil thereto lower than when the hydraulic oil issupplied from the acceleration cylinder 2 and the booster cylinder 3. Inthe injection cylinder 1, high pressure is applied to the piston 1P bythe hydraulic oil from the booster cylinder 3. The injection cylinder 1and injection plunger then gradually apply pressure into the cavity.Consequently, the pressure within the cavity is increased. This pressureincreasing step pressurizes and forms the molding material in thecavity.

The resistance applied from the cavity to the injection plunger andinjection cylinder 1 increases as the injection plunger and injectioncylinder 1 use the hydraulic oil from the booster cylinder 3 to increasethe pressure within the cavity. Consequently, the resistance istransmitted from the bottom chamber 1B of the injection cylinder 1 tothe booster cylinder 3 and acts as a load resistance onto the motor 10via the nut 12 and the ball screw 11. A load torque of the motor 10 ismonitored in the injection apparatus 100. When the load torque of themotor 10 becomes equal to or greater than a predetermined value, it isdetermined that the process of filling the cavity with the moldingmaterial is completed. Further, the injection apparatus 100 continues todrive the motor 10 to continuously apply pressure to the moldingmaterial in the cavity with a predetermined torque. Thereafter, when themolding material becomes solidified, the injection apparatus 100 stopsthe motor 10. After the molding material has solidified, the injectionapparatus 100 determines that the molding process is completed. Further,the injection apparatus 100 then takes out the molded article. At thismoment, when separating the movable mold from the fixed mold, theinjection apparatus 100 drives the motor 10 to apply a load to a part ofthe molded article in order to push the molded article out of the fixedmold. The molded article is demolded from the fixed mold in this manner.

Next, the injection apparatus 100 drives the motor to rotate reversely.The injection apparatus 100 then retracts the injection plunger and theinjection cylinder 1. As a result of reversely rotating the motor 10,the piston 2P of the acceleration cylinder 2 and the piston 3P of thebooster cylinder 3 are moved in the opposite direction by the ball screw11 and the nut 12. Consequently, in the acceleration cylinder 2, the rodchamber 2R is reduced in size and the bottom chamber 2B is increased. Atthe same time, in the booster cylinder 3, the rod chamber 3R is reducedin size and the bottom chamber 3B is increased. The injection apparatus100 drives the hydraulic pump 22 of the feed/discharge mechanism 20 topour hydraulic oil into the rod chamber 1R of the injection cylinder 1.When the hydraulic oil is supplied to the rod chamber 1R and the bottomchambers 2B and 3B of the acceleration cylinder 2 and booster cylinder 3are increased in size, the hydraulic oil flows out of the bottom chamber1B of the injection cylinder 1. At this moment, the pilot operated checkvalve 4 is opened in response to the application of the pilot pressurethrough the pilot conduit 4P, allowing the hydraulic oil to flow fromthe bottom chamber 1B to the bottom chamber 2B. As a result, the amountof hydraulic oil in the rod chamber 1R of the injection cylinder isincreased, while the amount of hydraulic oil in the bottom chamber 1B isdecreased, thereby moving the piston 1P. Subsequently, the injectioncylinder 1 and the injection plunger are retracted. Once the injectionplunger and the injection cylinder 1 are retracted to predeterminedpositions, the hydraulic oil no longer flows out of the bottom chamber1B of the injection cylinder 1. At this moment, the piston 2P of theacceleration cylinder 2 and the piston 3P of the booster cylinder 3 arenot yet returned to predetermined positions and therefore continue toreturn to the predetermined positions. The shortage of hydraulic oilwhich occurs due to the size increase of the bottom chambers 2B and 3Bis replenished with the hydraulic oil from the buffer tank 15 via thecheck valve 6. Once the piston 2P of the acceleration cylinder 2 and thepiston 3P of the booster cylinder 3 are retracted to the predeterminedpositions, one cycle of injection molding is ended.

The injection apparatus 100 of the present embodiment has the followingeffects.

(1) In the injection apparatus 100 of the present embodiment, theacceleration cylinder 2 and the booster cylinder 3 are disposed inparallel with each other with respect to the injection cylinder 1. Theacceleration cylinder 2 and the booster cylinder 3 are drivensynchronously by the motor 10, the ball screw 11 and the nut 12. Thus,the driving means comprising the single motor 10, ball screw 11 and nut12 can realize high injection speed and injection pressure.

(2) The driving means of the injection apparatus 100 is a singlestructure comprising the motor 10, the ball screw 11 and the nut 12.Compared to a construction in which the acceleration cylinder 2 and thebooster cylinder 3 are driven by a plurality of driving means, theconstruction of the present embodiment can reduce the number of partsand the cost of the injection apparatus 100. In addition, since only thesingle-structured driving means need be provided in the injectionapparatus 100, reduction in the space for and the size of the injectionapparatus 100 can be accomplished.

(3) The injection apparatus 100 is provided with the flow rateadjustment circuit 5. The flow of the hydraulic oil in the accelerationcylinder 2 can be easily switched by the flow rate adjustment circuit 5.

(4) The flow rate adjustment circuit 5 comprises the buffer tank 15, thecheck valve 6 and the pilot switching valve 16. The pilot switchingvalve 16 can be freely switched by means of the pilot pressure.Therefore, it is not necessary to provide the flow rate adjustmentcircuit 5 with new driving means, providing a simple structure of theflow rate adjustment circuit 5.

(5) The diameter D2 of the acceleration cylinder 2 is set to be greaterthan the diameter D3 of the booster cylinder 3. Therefore, when drivingthe injection cylinder 1, high-speed drive of the injection cylinder 1can be accomplished by supplying a larger amount of hydraulic oil byusing the piston 2P of the acceleration cylinder 2 with the largerdiameter D2. In addition, the diameter D3 of the booster cylinder 3 forapplying a necessary pressure to the injection cylinder 1 by means ofthe booster cylinder 3 can be set without consideration of the diameterD2 of the acceleration cylinder 2.

The present invention is not limited to the foregoing embodiment.Modifications of the present invention are described hereinbelow.

-   -   The acceleration cylinder 2 and the booster cylinder 3 according        to the embodiment employ different diameters and the same manner        stroke but are not limited to such construction. The size of        each cylinder can be changed as appropriate. For instance, the        diameter D2 of the acceleration cylinder 2 and the diameter D3        of the booster cylinder 3 may be equal to each other. The        diameter D2 may be smaller than the diameter D3. It is preferred        that the diameters of the pistons 2P and 3P be set appropriately        in accordance with the diameter D1 of the piston 1P of the        injection cylinder 1.    -   The flow rate adjustment circuit 5 is not limited to the        construction described in the embodiment. For example, an        electromagnetic switching valve may be used in place of the        pilot switching valve 16. Further, the above construction may        have a construction where the position of the injection cylinder        1 is detected with a limit switch or the like and the switching        valve is switched at a predetermined position of the injection        cylinder 1. Furthermore, the above construction may have a        construction where an encoder or the like is provided in the        motor 10 and the switching valve is switched based on the        driving amount of the motor 10 or the like. Also, a switching        valve may be used in place of the check valve 6. Further, a        hydraulic pump, etc., may be provided to adjust the flow rate of        the hydraulic oil.    -   The driving means according to the embodiment is not limited to        the structure of a ball screw. The construction of the driving        means may be changed as appropriate as long as it can        synchronously drive the piston 2P of the acceleration cylinder 2        and the piston 3P of the booster cylinder 3 by means of the        motor 10.    -   The rod chamber 1R of the injection cylinder 1, the rod chamber        2R of the acceleration cylinder 2 and the rod chamber 3R of the        booster cylinder 3 may be configured so that hydraulic oil is        fed into and discharged from their interiors.

EXPLANATION OF REFERENCE NUMERALS

1 Injection cylinder, 1B Bottom chamber, 1P Piston, 1Pa Piston rod, 1RRod chamber, 2 Acceleration cylinder, 2B Bottom chamber, 2P Piston, 2RRod chamber, 3 Booster cylinder, 3B Bottom chamber, 3P Piston, 3R Rodchamber, 4 Pilot operated check valve, 4P Pilot conduit, 5 Flow rateadjustment circuit, 6 Check valve, 10 Motor, 11 Ball screw, 12 Nut, 15Buffer tank, 16 Pilot switching valve, 16P Pilot conduit, 100Die-casting machine (injection apparatus).

1. An injection apparatus, comprising: an injection cylinder driving aninjection plunger to inject a molding material; a first cylinderconnected to the injection cylinder, the first cylinder feedinghydraulic oil to the injection cylinder and draining hydraulic oiltherefrom; a second cylinder connected to the injection cylinder inparallel with the first cylinder, the second cylinder feeding hydraulicoil to the injection cylinder and draining hydraulic oil therefrom; asingle unit of driving means for reciprocatingly driving a piston of thefirst cylinder and a piston of the second cylinder; a directionalcontrol valve provided between one end of the injection cylinder and oneend of the first cylinder, the directional control valve allowing a flowof hydraulic oil from the first cylinder toward the injection cylinderbut cutting off the flow of hydraulic oil from the injection cylindertoward the first cylinder; flow rate adjustment means provided betweenthe directional control valve and the first cylinder, the flow rateadjustment means being for adjusting a flow rate of hydraulic oilbetween the one end of the first cylinder and the one end of theinjection cylinder, and wherein the driving means drives the piston ofthe first cylinder and the piston of the second cylinder insynchronization with each other.
 2. The injection apparatus according toclaim 1, wherein the flow rate adjustment means includes: a buffer tankcapable of temporarily storing hydraulic oil; a pilot switching valvecapable of discharging to the buffer tank the hydraulic oil presentbetween the directional control valve and the first cylinder; and areplenishment control valve supplying the hydraulic oil in the buffertank between the directional control valve and the first cylinder whenthere is insufficient hydraulic oil between the directional controlvalve and the first cylinder.
 3. The injection apparatus according toclaim 1, wherein a cylinder diameter of the first cylinder is greaterthan that of the second cylinder.